As authorities are investigating the shooting rampage at a midnight showing of "The Dark Knight Rises" in an Aurora, Col., movie theater, details are emerging about James Holmes, the 24-year-old who allegedly donned riot gear and stalked the aisles with a rifle.

Psychology experts say it's hard to know what Holmes's state of mind was before his alleged rampage, but emerging details suggest he was a deeply disturbed individual.

"He said he was the Joker," one law enforcement official told ABC News, referring to a villain from the Batman series. New York Police Commissioner Ray Kelly said the suspect had dyed his hair red to match the character's.

Witnesses said a shooter entered the movie theater about 20 or 30 minutes into the film, dressed in a riot helmet, bulletproof vest and a gas mask, and carrying a rifle and a handgun. He set off what's been reported as a smoke bomb, then began methodically stalking the aisles, shooting patrons at random as some tried to flee.

Authorities report that 12 people were killed and nearly 50 were injured. Holmes was arrested in the parking lot of the movie theater, looking like "a villain in a movie," a Congressional official briefed on the situation told ABC News. His apartment is filled with explosives and being searched by Hazmat teams.

Kaitlyn Fonzi, who lives directly below Holmes's Aurora apartment, told ABC News that around midnight, she heard very loud music coming from the apartment above her.

The "same techno song that sounded like it included gunshots was playing in a loop for a long time," she said.

Fonzi said the music abruptly stopped at about 1 a.m.

ABC News has confirmed that Holmes was a PhD student in the neuroscience department of the University of Colorado at Denver. In a statement, the university said Holmes was in the process of withdrawing from the program after enrolling in June 2011.

It's not clear whether he had a history of violence or psychotic behavior, but Holmes's mother told ABC News that she felt that her son was likely the culprit.

"You have the right person," she said in a phone interview from her San Diego home.

As the investigation continues, psychologists say it's likely that certain parts of Holmes's life and behavior will emerge that point to signs warnings of his actions. But those warning signs may not have been necessarily obvious indications of violence.

ABC News spoke with several psychologists, none of whom has direct knowledge of Holmes.

"This is not a person that gets in bar fights and hurts other people," said Dr. Stevan Hobfoll, a professor of behavioral sciences at Rush University Medical Center in Chicago. "They're more likely to make statements about how they're going to get people. Those people are going to see they'll know who he is, and they'll be sorry."

"In general, these people tend to be socially inept and alienated from the mainstream," said Dr. Felipe Amunategui, an associate training director for child and adolescent psychiatry at University Hospitals Case Medical Center in Cleveland.

Psychologists said shooters who go on rampages, targeting random people with no apparent motive, may or may not have a psychotic disorder such as schizophrenia. Rather, Holmes was likely living in a world of an alternate reality, suffering from delusions of threats and making plans to make right things that he perceived were wrong.

"The thing to realize is that within his own thoughts, what he was doing was completely logical. To him, he was accomplishing something worth doing," said Dr. E. Fuller Torrey, founder of the Treatment Advocacy Center in Arlington, Va.

Amunategui said it's likely that Holmes had been obsessively thinking about his plan until some unknown event spurred him to action.